In recent years, in view of energy saving and environmental conservation, illumination apparatuses (such as light-emitting diode lamps) using a light-emitting diode (hereinafter also referred to as “LED”) as a light source have been increasingly used in place of incandescent lamps. Conventional illumination apparatuses using LEDs as the light source, however, emit light only in the forward direction, and cannot emit light in a wide range unlike incandescent lamps. Therefore, unlike incandescent lamps, the conventional illumination apparatuses cannot illuminate a room over a wide range by utilizing the reflection light of the ceiling and walls.
To make the light distribution characteristics of the conventional illumination apparatuses using LEDs as the light source close to the light distribution characteristics of incandescent lamps, it has been proposed to control the light distribution of light emitted from LEDs by a light flux controlling member (see, for example, PTL 1). FIG. 1 is a schematic view illustrating a configuration of illumination apparatus 10 disclosed in PTL 1. As illustrated in FIG. 1, illumination apparatus 10 includes a plurality of LEDs 12 disposed on a substrate, and cylindrical case 14 made of a light transmissive material disposed around LEDs 12. The top surface of case 14 is formed in an inverted truncated cone shape. Aluminum plate (light flux controlling member) 16 that reflects light is bonded on the tilted surface of the truncated cone, and the tilted surface functions as a reflecting surface. On the other hand, the planar surface of the truncated cone shape functions as transmission window 18 through which light passes. As indicated by an arrow in FIG. 1, part of light emitted from LED 12 disposed at the center passes through transmission window 18 and becomes emission light in the forward (upward) direction. In addition, part of light emitted from LEDs 12 is reflected by aluminum plate 16 and becomes emission light in the lateral direction (horizontal direction) and the rearward direction (lower direction).
By controlling the travelling direction of the light emitted from the LED disposed at the center with use of a light flux controlling member, it is possible to obtain not only emission light in the forward direction but also emission light in the lateral direction and the rearward direction. Accordingly, by use of the light flux controlling member (aluminum plate) disclosed in PTL 1, it is possible to make the light distribution characteristics of an illumination apparatus (LED lamp) close to the light distribution characteristics of incandescent lamps to a certain degree.